Synergistic Plant–mycorrhizal Interactions for Heavy Metal Remediation in Crude Oil–contaminated Tropical Soils

Petroleum hydrocarbon contamination poses a major threat to soil quality in tropical ecosystems by altering physicochemical properties and enhancing heavy metal toxicity. This study evaluated the interactive effects of plant species, arbuscular mycorrhizal fungi (AMF), and crude oil contamination on soil properties, heavy metal dynamics, and root accumulation patterns. A pot experiment was arranged in a two-factor factorial Completely Randomized Design with three replications using three indigenous species (Chromolaena odorata, Aspilia africana, and Eupatorium capillifolium) grown in soils amended with 0 ml, 400 ml, and 800 ml crude oil per 10 kg soil, with or without AMF. Crude oil significantly modified soil physical properties by increasing sand content from 827.00±13.00 to 915.00±13.00 gkg⁻¹, while reducing silt and clay to as low as 32.00±4.00 and 48.00±5.00 gkg⁻¹, respectively. Soil pH remained acidic (4.50–5.40). Available phosphorus declined with increasing crude oil, from 42.80±1.48 mgkg⁻¹ in C. odorata (soil + plant) to 18.90±2.48 mgkg⁻¹ in A. africana with AMF and 800 ml crude oil. Organic carbon and organic matter increased markedly at higher oil levels, reaching 35.51±5.93 gkg⁻¹ and 61.22±2.37 gkg⁻¹, respectively. Soil cadmium and nickel varied significantly, with the highest Ni concentration (16.09±2.84 mgkg⁻¹) recorded under E. capillifolium with AMF and 800 ml crude oil, while chromium remained below detectable limits in soil. Root metal accumulation was strongly species